Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Content, such as audio or video information, electronic books, Internet publications, etc. may be output by different content output devices. For example, content may be output to a user through an audio player, speaker, radio, computer, cell phone, augmented reality device, etc. In general, these types of content output devices create waves that are discernable by a human. The content may be available from more than one source.